5 - Mitochondria and Oxidative Phosphorylation Flashcards
What is the theory of endosymbiosis? and why does this explain mitochondria having their own DNA
- Ancestral eukaryotic cell engulfed an aerobic bacterium (mitochondria) by endocytosis
- The cell could provide the bacterium with resources and the bacterium could provide the cell energy from oxygen
- forming a symbiotic relationship
- As a result mitochondria have their own genome and biosynthetic machinery for making RNA and Proteins
Describe the mitochondrial genome
- Singular circular chromosome
- Located in the matrix
- 37 genes in total: 2 rRNA, 22tRNA, 13 protein encoding
- very small compared to nuclear genome
what happens to male mitochondrial DNA?
- It is degraded as soon as the sperm fertilises the egg, so we only have maternal Mitochondrial DNA
Talk about mitochondrial fission and fusion
- Mitochondria are constantly fusing and dividing
- if for example 2 mitochondria fuse, then 1 large mitochondria will have 3 copies of mtDNA
how does mtDNA replicate
- randomly
- just before fission mtDNA localise to mitochondrial polarities, to ensure they are incorporated into the new one
definition of Mitochondrial Biogenesis
the increase in abundance of mt proteins, mtDNA and mitochondrial numbers
when does mitochondrial biogenesis occur
when cells are stressed and need to produce more ATP
- eg during exercise
Describe the mitochondrial ribosome and the link to the mitochondrial genome
- There are 2 rRNA genes in the mitochnodrial genome
- rRNA form the subunits of ribosomes
- Large 39s subunit made of 50 proteins
- Small 28s subunit made of 30 proteins
- Overall 55s and 80 proteins
what does s indicate
- how fast they fall in a tube of suspension
55s mitochondrial ribosomes synthesise proteins coded by mtDNA, but mitochondria need more proteins than they can make to survive, where do these proteins come from
- cytosolic/cytoplasmic Ribosomes
is the inner mitochondrial membrane very permeable or impermeable
- inner is very impermeable
- outer is more permeable
Describe how precursor proteins in the cytoplasm enter the mitochondrial matrix
- chaperone proteins bind to the precursor protein and prevent it from folding so it can be pulled into the matrix
- The special signal sequence on the precursor protein binds to a receptor protein in TOM complex on outer mt membrane
- TOM pulls the protein across the outer membrane into the intermembrane space
- The special signal sequence then binds to TIM 23 complex which translocates the precursor protein across the inner membrane
- the chaperone protein is then lost and the special signal sequence cleaved leaving the protein to fold
what enzyme cuts off the special signal sequence from the precursor protein
- signal peptidase
What do TOM and TIM stands for and where are they located
TOM - Translocase Outer-Membrane complex
Tim - Translocase Inner Membrane complex
What is a special signal sequence
- a specific series of amino acids recognised by a specific receptor
How does Pyruvate transport into the mitochondrial matrix from the cytoplasm
- Pyruvate is small enough to travel through porins in the outer mitochondrial membrane
- Pyruvate then travels from the intermembrane space into the matrix through Mitochondrial Pyruvate Carriers
what happens to pyruvate once its in the matrix
- pyruvate is decarboxylated to form Acetyl CoA
How do Fatty acids transport into the Mitochondrial Matrix
- Fatty acids cannot cross either mt membrane so have to be converted
1) Fatty acid is combined with CoA forming fatty Acyl CoA in an unfavourable reaction costing 1 ATP
2) fatty Acyl CoA is then combined with carnitine via the enzyme CPT1 located on the outer mt membrane, this forms Acyl-Carnitine
3) Acyl-Carnitine can travel through porins through the outer mt membrane
4) Acyl-Carnitine is then transported into the matrix through the protein translocase which is an antiporter which moves carnitine out of the matrix at the same time
What happens to Acyl-Carnatine once it is in the matrix
Acyl-Carnitine in converted back into fatty Acyl CoA and carnitine by CPT 2, Carnitine is then shipped out of the matrix through the protein translocase antiporter
Where are CPT1, CPT2, porins and protein translocase located?
CPT1 and Porins - Outer mitochondrial membrane
CPT 2 and Protein translocase - Inner mt membrane
What do the proteins CPT1, CPT2, porins and protein translocase do or transport?
CPT1 : Combines fatty acyl CoA and Carnitine to produce Acyl-Carnitine
CPT2: Converts Acyl-Carnitine back into fatty acyl CoA and Carnitine
porins: Acyl Carnitine
protein translocase: Acyl carnitine
How is NADH transported into the the mitochondria
The Malate-Aspartate shuttle
- Oxaloacetate in the intermembrane space is reduced to malate through the oxidation of NADH
- Malate can travel into the matrix through an antiporter protein with a-ketoglutarate
- Malate is now oxidised into oxaloacetate again, which in return reduces NAD+ into an NADH
- Oxaloacetate is transaminated into aspartate, while glutamate is converted into a-ketoglutarate
- Aspartate can travel back into the intermembrane space through an antiporter when glutamate enters the matrix
- Aspartate is then transaminated back into oxaloacetate and a-ketoglutarate is converted into glutamate
what enzyme catalyses transamination of oxaloacetate and aspartate
- transaminase
where does the malate aspartate shuttle occur
across the inner mitochondrial membrane
